System and method of controlling an oil flow within a refrigeration system

ABSTRACT

A system and method of controlling an oil flow within a refrigeration system, the system including a compressor, an expansion device in flow communication with the compressor, and an electronic controller in communication with the expansion device and the compressor, wherein the electronic controller is configured to operate in an oil return mode based at least in part on an operational speed and a continuous operational run time of the compressor.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is related to, and claims the priority benefit of, U.S. Provisional Patent Application Ser. No. 62/232,274 filed Sep. 24, 2015, the contents of which are hereby incorporated in their entirety into the present disclosure.

TECHNICAL FIELD OF THE DISCLOSED EMBODIMENTS

The presently disclosed embodiments generally relate to refrigeration systems, and more particularly, to a system and method of controlling an oil flow within a refrigeration system.

BACKGROUND OF THE DISCLOSED EMBODIMENTS

Generally, in refrigeration compressors, oil and refrigerant mix continuously. Refrigeration oils are soluble in liquid refrigerant and at normal room temperatures they will mix completely. Since oil typically must pass through the compressor to provide lubrication, a small amount of oil is typically in circulation with the refrigerant. Typically, oil and refrigerant vapor do not mix readily, and the oil can be properly circulated through the system typically only if gas velocities are high enough to sweep the oil along In some refrigeration compressors, for example inverter compressors, if refrigerant velocities are not sufficiently high, oil will tend to coat the walls of the evaporator tubing, decreasing heat transfer and possibly causing a shortage of oil in the compressor. Oil recovering devices are generally used in order to recover the oil; however, the addition of such devices increase the costs and size of the refrigeration system

Accordingly, there exists a need for a system and method of recovering oil when refrigerant velocities may not supply adequate oiling to the compressor.

SUMMARY OF THE DISCLOSED EMBODIMENTS

In one aspect a refrigeration system is provided. The refrigeration system includes a compressor, an expansion device in flow communication with the compressor, and an electronic controller in communication with the expansion device and the compressor. The electronic controller is configured to operate in an oil return mode based at least in part on an operational speed and a continuous operational run time of the compressor. In an embodiment, the electronic controller is further configured to command the compressor to operate at the minimal speed limit for an oil return duration of time if it is determined that the operational speed is less than the minimal speed limit and the continuous operational run time is greater than or equal to the run time limit, and command the expansion device to operate in order to decrease a target superheat value by an oil return target value if it is determined that the operational speed is less than the minimal speed limit and the continuous operational run time is greater than or equal to the run time limit.

In an embodiment, to operate in an oil return mode, the electronic controller is configured to determine whether the operational speed is less than a minimal speed limit, and determine whether the continuous operational run time is greater than or equal to a run time limit.

In one embodiment of the system, the minimal speed limit is approximately 3000 revolutions per minute. In one embodiment of the system, the run time limit is approximately 45 minutes. In one embodiment, the oil return duration of time is approximately 10 minutes. In one embodiment of the system, the oil return target value is approximately 5 degrees Fahrenheit.

In one aspect, an electronic controller is provided. The electronic controller includes a processor, and a memory, wherein the processor is configured to operate a program stored in memory, the program configured to command a compressor to operate at a demand operational speed, determine whether the compressor has operated at a speed less than a minimal speed limit for a continuous duration of time greater than or equal to a run time limit, and operate in an oil return mode if the compressor has operated at a speed less than the minimal speed limit for a continuous duration of time greater than or equal to the run time limit. In one embodiment of the controller, to operate in an oil return mode, the program is further configured to command the compressor to operate at the minimal speed limit for an oil return duration of time, and command an expansion device to operate in order to decrease a target superheat value by an oil return target value.

In one embodiment of the controller, the minimal speed limit is approximately 3000 revolutions per minute. In one embodiment of the controller, the run time limit is approximately 45 minutes. In one embodiment of the controller, the oil return duration of time is approximately 10 minutes. In one embodiment of the controller, the oil return target value is approximately 5 degrees Fahrenheit.

In one aspect, a method of controlling oil flow within a compressor is provided. The method includes operating the compressor at a demand operational speed, operating the controller to determine whether the compressor has operated at a speed less than a minimal speed limit for a continuous duration of time greater than or equal to a run time limit, and operating the controller to enter an oil return mode if the compressor has operated at a speed less than the minimal speed limit for a continuous duration of time greater than or equal to the run time limit. In an embodiment of the method, the oil return mode includes operating the compressor at the minimal speed limit for an oil return duration of time, and controlling the expansion device to decrease a target superheat value by an oil return target value.

In one embodiment of the method, the minimal speed limit is approximately 3000 revolutions per minute. In one embodiment of the method, the run time limit is approximately 45 minutes. In one embodiment of the method, the oil return duration of time is approximately 10 minutes. In one embodiment of the method, the oil return target value is approximately 5 degrees Fahrenheit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates a schematic diagram of a refrigerant system according to an embodiment of the present disclosure;

FIG. 2 illustrates a schematic flow diagram of a method of controlling oil flow within the compressor according to an embodiment of the present disclosure; and

FIG. 3 illustrates a schematic flow diagram of an oil return mode according to an embodiment of the present disclosure.

DETAILED DESCRIPTION OF THE DISCLOSED EMBODIMENTS

For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of this disclosure is thereby intended.

FIG. 1 schematically illustrates an embodiment of a refrigerant system, generally indicated at 10. The refrigerant system includes a compressor 12 configured to deliver compressed refrigerant downstream to a heat rejection heat exchanger 14 (e.g. a condenser). The compressed refrigerant passes through an expansion device 16 (e.g. an electronic expansion valve to name one non-limiting example) and flows in sequence through an evaporator 18, and through a suction line 22 back to the compressor 12. A temperature sensor 24 may be placed on the suction line entering the compressor 22. The temperature sensor 24 is configured to measure a suction gas temperature entering the compressor. A pressure sensor 28 may also be placed on the suction line to measure a suction pressure of the refrigerant entering the compressor 22.

The temperature sensor 24 is operably coupled to and communicates with an electronic controller 26. The electronic controller 26 is configured to command the refrigerant system 10 to enter an oil return mode under certain conditions. The electronic controller 26 is further coupled to, and configured to control the expansion device 16 to adjust and control a target superheat. Target superheat is the recommended superheat for the given indoor and outdoor environmental conditions based on an outdoor dry-bulb temperature and an indoor wet-bulb temperature. Sensors 24 and 28 are operably coupled to suction line 22 between the exit from the evaporator 18 and inlet to the compressor 12, and are in communication with the electronic controller 26. Sensors 24 and 28 are configured to measure a suction superheat value. The sensor 28 may measure the suction pressure that would be used by the electronic controller 26 to determine the saturated refrigerant temperature. Superheat is the difference between the actual refrigerant temperature at sensor 24 and the saturated refrigerant temperatures at approximately the same location. It will be appreciated that sensor 28 can be any other type of sensor typically used to measure a superheat value.

FIG. 2 illustrates a method of controlling an oil flow within the compressor 12, the method generally indicated at 100. The method includes step 102 of operating the compressor 12 at a demand operational speed. For example, based on the demand of the refrigerant system 10, the compressor 12 may operate at a plurality of non-zero operating speeds to satisfy the demand.

The method 100 further includes step 104 of operating the controller 26 to determine whether the compressor 12 has operated at a speed less than a minimal speed limit for a continuous duration of time greater than or equal to a run time limit. The minimal speed limit may be a pre-determined operational speed threshold at which oil does not adequately flow through the compressor 12. The run time limit may be a pre-determine time threshold which may begin to affect the flow of oil within the compressor 12. It will be appreciated that if the demand of the system 10 changes before the expiration of the run time limit, the controller 26 adjusts the speed of the compressor 12 to meet the new demand, and returns to step 102.

In an embodiment, the minimal speed limit is approximately 3000 revolutions per minute (RPM). In some embodiments, the minimal speed limit is adjustable, and may be greater than or less than 3000 RPM. In one embodiment, the run time limit is approximately 45 minutes. In some embodiments, the run time limit is adjustable, and may be greater than or less than 45 minutes.

The method 100 further includes step 106 of operating the controller 26 to enter an oil return mode if the compressor 12 has operated at a speed less than the minimal speed limit for a continuous duration of time greater than or equal to the run time limit. In an embodiment, as shown in FIG. 3, operating in an oil return mode includes step 202 of operating the compressor 12 at a speed equal to the minimal speed limit for an oil return duration of time, and step 204 of controlling the expansion device 16 to decrease a target superheat value by an oil return target value. After the controller 26 completes the oil return mode, the method returns to step 102 of operating the compressor 12 at the demand operational speed.

In an embodiment, the oil return duration of time is approximately 10 minutes. In some embodiments, the oil return duration of time is adjustable, and may be greater than or less than 10 minutes. In one embodiment, the oil return target value is approximately 5 degrees Fahrenheit (° F.) (approximately 2.8 degrees Celsius). In some embodiments, the oil return target value is adjustable and may be greater than or less than 5° F. (approximately 2.8 degrees Celsius).

In one non-limiting example of the method 100, if the demand is such that the compressor 12 has operated at a speed less than 3000 RPM and for a duration of at least 45 minutes, the controller 26 commands the compressor 12 to enter an oil return mode by increasing the speed of the compressor 12 to the minimal speed limit (e.g. 3000 RPM). The controller 26 also commands the adjustment of the expansion device 16 to lower the target superheat of the system 10 by approximately 5° F. Lowering the superheat target improves the solubility of the refrigerant-oil mixture, and increasing the compressor speed increases the refrigerant velocities to a sufficient level to allow the oil to return to the compressor 12. The controller 26 operates the system 10 in the oil return mode for approximately 10 minutes; then, returns to the operational speed to meet the demand of the system 10.

It will therefore be appreciated that the present embodiments includes a method of returning oil to the compressor 12 by increasing the speed of the compressor 12 to the minimal speed limit for an oil return duration of time and decreasing the superheat target by an oil return target value.

While the present disclosure has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only certain embodiments have been shown and described and that all changes and modifications that come within the spirit of the present disclosure are desired to be protected. 

What is claimed is:
 1. A method of controlling oil flow within a compressor, the compressor operably coupled to a controller and an expansion device, the method comprising: (a) operating the compressor at a demand operational speed; (b) operating the controller to determine whether the compressor has operated at a speed less than a minimal speed limit for a continuous duration of time greater than or equal to a run time limit; and (c) operating the controller to enter an oil return mode if the compressor has operated at a speed less than the minimal speed limit for a continuous duration of time greater than or equal to the run time limit.
 2. The method of claim 1, wherein the minimal speed limit is approximately 3000 revolutions per minute.
 3. The method of claim 1, wherein the run time limit is approximately 45 minutes.
 4. The method of claim 1, wherein the oil return mode comprises: (i) operating the compressor at the minimal speed limit for an oil return duration of time; and (ii) controlling the expansion device to decrease a target superheat value by an oil return target value.
 5. The method of claim 4, wherein the oil return duration of time is approximately 10 minutes.
 6. The method of claim 4, wherein the oil return target value is approximately 5 degrees Fahrenheit.
 7. An electronic controller comprising: a processor, and a memory, wherein the processor is configured to operate a program stored in memory, the program configured to: (a) command a compressor to operate at a demand operational speed; (b) determine whether the compressor has operated at a speed less than a minimal speed limit for a continuous duration of time greater than or equal to a run time limit; and (c) operate in an oil return mode if the compressor has operated at a speed less than the minimal speed limit for a continuous duration of time greater than or equal to the run time limit.
 8. The electronic controller of claim 7, wherein the minimal speed limit is approximately 3000 revolutions per minute.
 9. The electronic controller of claim 7, wherein the run time limit is approximately 45 minutes.
 10. The electronic controller of claim 7, wherein to operate in an oil return mode, the program is further configured to: (i) command the compressor to operate at the minimal speed limit for an oil return duration of time; and (ii) command an expansion device to operate in order to decrease a target superheat value by an oil return target value.
 11. The electronic controller of claim 10, wherein the oil return duration of time is approximately 10 minutes.
 12. The electronic controller of claim 10, wherein the oil return target value is approximately 5 degrees Fahrenheit.
 13. A refrigeration system comprising: a compressor; an expansion device in flow communication with the compressor; and an electronic controller in communication with the expansion device and the compressor; wherein the electronic controller is configured to operate in an oil return mode based at least in part on an operational speed and a continuous operational run time of the compressor.
 14. The refrigeration system of claim 13, wherein to operate in an oil return mode, the electronic controller is configured to: (a) determine whether the operational speed is less than a minimal speed limit; and (b) determine whether the continuous operational run time is greater than or equal to a run time limit;
 15. The refrigeration system of claim 14, wherein the minimal speed limit is approximately 3000 revolutions per minute.
 16. The refrigeration system of claim 14, wherein the run time limit is approximately 45 minutes.
 17. The refrigeration system of claim 14, wherein the electronic controller is further configured to: (i) command the compressor to operate at the minimal speed limit for an oil return duration of time if it is determined that the operational speed is less than the minimal speed limit and the continuous operational run time is greater than or equal to the run time limit; and (ii) command the expansion device to operate in order to decrease a target superheat value by an oil return target value if it is determined that the operational speed is less than the minimal speed limit and the continuous operational run time is greater than or equal to the run time limit.
 18. The refrigeration system of claim 17, wherein the oil return duration of time is approximately 10 minutes.
 19. The refrigeration system of claim 17, wherein the oil return target value is approximately 5 degrees Fahrenheit. 